## Difference between real and ideal gas

$PV=nRT$

Sarah_Hoffman_2H
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### Difference between real and ideal gas

Can someone explain the difference between a real and ideal gas?

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### Re: Difference between real and ideal gas

An ideal gas is based on certain assumptions of the Kinetic Molecular Theory. For an ideal gas, it is assumed that the molecules are constantly in motion, they have negligible volume, they do not exert any force on each other, and that they have perfectly elastic collisions. These assumptions allow the ideal gas law to be used. However, real gas molecules do have volume, do exert a force on each other, and they have non-elastic collisions. So the real gas law would be (P+((an^2)/V^2))(V – n b ) = nRT, to account for those factors. Real gases act most like ideal gases at low pressures, high temperatures, and a low number of moles.

Hope this helps!

Ivy Tan 1E
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### Re: Difference between real and ideal gas

Hi!
An ideal gas has negligible volume, particles that do not collide because they are in constant motion, and particles that exhibit no attraction or repulsion because they do not interact with each other. A real gas violates all of these criteria: it has volume and has particles that collide and interact with each other. Hope this was helpful!!

Vanshika Bhushan 1A
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### Re: Difference between real and ideal gas

Ideal gases abide by all gas laws regardless of the pressure of temperature. Ideal gases occupy no volume. Real gases occupy small volumes. Ideal gas particles exert no attractive forces and their collisions are elastic. Real gases exert small attractive forces. The pressure of an ideal gas is greater than that of a real gas because its particles lack the attractive forces that hold the particles back when they collide.

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### Re: Difference between real and ideal gas

Although the last few posts appropriately described the difference between ideal gases and real gases, I wanted to bring up a really simple and useful way to quantify how "ideal" a gas really is -- its compressibility. The compression factor (Z) of a gas can be found by comparing the molar volume of a real gas to the molar volume of an ideal gas at the same temperature and pressure. Therefore, the compression factor of an ideal gas would be 1. By plotting the compression factor of the real gas against the ideal gas over various temperature and pressure values, we obtain a graph that we can then use to account for the "real" factors of a gas while doing ideal gas calculations.

Hope this was interesting!

Grace_Remphrey_2J
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### Re: Difference between real and ideal gas

Here's a table I find super helpful when looking at the difference between real and ideal gas. Hope this helps!

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### Re: Difference between real and ideal gas

As a follow-up question, if real and ideal gasses are so different than each other, why is it helpful to treat real gasses the same as ideal gasses? Would this assumption not cause problems?

Mingzi Yang 1E
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### Re: Difference between real and ideal gas

Grace_Remphrey_2J wrote:Here's a table I find super helpful when looking at the difference between real and ideal gas. Hope this helps!
Screen Shot 2021-01-10 at 3.26.10 PM.png

This table is helpful! Thank you!

AlbertGu_2C
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### Re: Difference between real and ideal gas

Jaden Joodi 3J wrote:As a follow-up question, if real and ideal gasses are so different than each other, why is it helpful to treat real gasses the same as ideal gasses? Would this assumption not cause problems?

I have the same question, because wouldn't the violations of the ideal gas law that the real gas law presents greatly interfere with the accuracy of the Ideal Gas Law's assumptions?

Ayesha Aslam-Mir 3C
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Joined: Wed Sep 30, 2020 9:43 pm

### Re: Difference between real and ideal gas

Shreyank Kadadi 3K wrote:Although the last few posts appropriately described the difference between ideal gases and real gases, I wanted to bring up a really simple and useful way to quantify how "ideal" a gas really is -- its compressibility. The compression factor (Z) of a gas can be found by comparing the molar volume of a real gas to the molar volume of an ideal gas at the same temperature and pressure. Therefore, the compression factor of an ideal gas would be 1. By plotting the compression factor of the real gas against the ideal gas over various temperature and pressure values, we obtain a graph that we can then use to account for the "real" factors of a gas while doing ideal gas calculations.

Hope this was interesting!

There's a Redlich-Kwong equation that involves pressure, temperature, and volume when working with gases.When factoring in compressibility, you get an equation that applies to pure substances. Not entirely relevant right now to the course but you can see https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Map%3A_Physical_Chemistry_(McQuarrie_and_Simon)/16%3A_The_Properties_of_Gases/16.02%3A_van_der_Waals_and_Redlich-Kwong_Equations_of_State

Armen_Isayan_2L
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### Re: Difference between real and ideal gas

The difference between a real and ideal gas, is that an ideal gas has no definite volume while a real gas has an established and definite volume. Also while analyzing the collisions which take place between the particles in both real and ideal gases, the real gases have non-elastic collisions and ideal gases have elastic collisions. In which case, real gases interact with other particles and ideal gases are independent of other particles. It is also important to note that ideal gases have higher pressure in comparison to real gases.

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